Abraham, Isaac, and Jacob are referred to as the three patriarchs of the people of Israel, and the period in which they lived is called the Patriarchal Age.

The word has mainly taken on specific ecclesiastical meanings. In particular, the highest-ranking bishops in Eastern Orthodoxy, Oriental Orthodoxy, the Roman Catholic Church (above Major Archbishop and primate), and the Assyrian Church of the East are called patriarchs. The office and ecclesiastical conscription (comprising one or more provinces, though outside his own (arch) diocese he is often without enforceable jurisdiction, unlike the Pope, the Bishop of Rome) of such a patriarch is called a patriarchate. Historically, a Patriarch may often be the logical choice to act as Ethnarch, representing the community that is identified with his religious confession within a state or empire of a different creed (as Christians within the Ottoman Empire).

According to Mormonism, a patriarch is one who has been ordained to the office of Patriarch in the Melchizedek Priesthood. The term is considered synonymous with the term evangelist. One of the patriarch’s primary responsibilities is to give Patriarchal blessings, as Jacob did to his twelve sons in the Old Testament. In the main branch of Mormonism, The Church of Jesus Christ of Latter-day Saints, Patriarchs are typically assigned in each stake and hold the title for life.

Patriarchs are also an eccelestial rank in a series of books by David Eddings, The Elenium and The Tamuli.

http://education.yahoo.com/reference/dictionary/entry/patriarch